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Nayek, Prasenjit,Mukherjee, Amrita,Jeong, Heon,Kang, Shin-Woong,Lee, Seung Hee,Yokoyama, Hiroshi American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.6
<P>We have studied the phase behavior of blue phase liquid crystal (BPLC)-unfunctionalized nanoparticle (NP) blends. Two different types of NPs which have different anchoring properties have been studied. Interestingly, Silica NP doped BPLC blends have revealed a small but clear positive shift of the Isotropic-BP phase transition temperature for lower concentration of NPs whereas with higher percentage of NPs we have observed a mixed phase consisted with chiral nematic (N*) and BP. On the other hand, low concentration polyhedral oligomeric silsesquioxanes (POSS) NPs which have stronger anchoring force than Silica NPs have enabled BP to stabilize thermally. Our experimental results agrees with the recent theory predicted that NP-defect interaction strongly depends on the interfacial energy between NP and LC which may be responsible for the observed effects in unfunctionalized NP-BPLC composite system.</P>
P. Nayek,S. Ghosh,S. Kundu,T. Pal Majumder,S.K. Roy,N. Bennis,J.M. Otón,R. Dabrowski 한국물리학회 2010 Current Applied Physics Vol.10 No.2
The electro-optical behavior of the orthoconic antiferroelectric liquid crystal mixture W-182 has been studied. Surface-stabilized, low thickness cells of this mixture give a perfect double hysteresis loop with 1 Hz triangular signal, reaching different transmission levels for different voltages amplitudes. These levels can be stabilized with a single holding voltage, making it possible for the material to be passively multiplexed at video rate. With the application of bias field at three different temperatures, we have observed the field-induced Fréedericksz transition from SmI*A–SmC*A, antiferroelectric to ferroelectric, and ferroelectric to paraelectric transition. Such Fréedericksz transition point is decreased with the increase of temperature.
Sudarshan Kundu,Taponita Datta (nee Ray),Prasenjit Nayek,Tapas Pal Majumder,Subir Kumar Roy 한국물리학회 2008 Current Applied Physics Vol.8 No.5
Liquid crystal mixtures of non-mesogenic polar molecule with a commercial ferroelectric liquid crystal (FLC) mixture were prepared. Two mixtures were prepared by mixing 0.5% (w/w) and 1% (w/w) of polar molecules with commercial FLC mixture. Comprehensive studies of dielectric and electro-optic properties of the commercial FLC mixture and the polar molecules doped FLC mixtures have been made as a function of temperatures. Our studies reveal a higher tilt angle in lower concentration (0.5%) mixture but in case of 1% mixture tilt angle is decreased in comparison to 0.5% mixture. The spontaneous polarization of the commercial FLC mixture and other two mixtures is almost equal in magnitude at all temperatures. At the lower temperature region of SmC* phase, Goldstone mode (GM) dielectric strength of the commercial FLC mixture and low concentration (0.5%) mixture is found almost equal but it is slightly higher in case of high concentration (1%) mixture. With the increase of temperature GM dielectric strength of both the doped mixtures rapidly converges at different temperatures which are much lower than the temperature of transition (TC) from SmC* – SmA phase. The results have been discussed. Liquid crystal mixtures of non-mesogenic polar molecule with a commercial ferroelectric liquid crystal (FLC) mixture were prepared. Two mixtures were prepared by mixing 0.5% (w/w) and 1% (w/w) of polar molecules with commercial FLC mixture. Comprehensive studies of dielectric and electro-optic properties of the commercial FLC mixture and the polar molecules doped FLC mixtures have been made as a function of temperatures. Our studies reveal a higher tilt angle in lower concentration (0.5%) mixture but in case of 1% mixture tilt angle is decreased in comparison to 0.5% mixture. The spontaneous polarization of the commercial FLC mixture and other two mixtures is almost equal in magnitude at all temperatures. At the lower temperature region of SmC* phase, Goldstone mode (GM) dielectric strength of the commercial FLC mixture and low concentration (0.5%) mixture is found almost equal but it is slightly higher in case of high concentration (1%) mixture. With the increase of temperature GM dielectric strength of both the doped mixtures rapidly converges at different temperatures which are much lower than the temperature of transition (TC) from SmC* – SmA phase. The results have been discussed.
Taponita Datta (nee Ray),Sudarshan Kundu,Prasenjit Nayek,Tapas Pal Majumder,Subir Kumar Roy,W. Haase 한국물리학회 2009 Current Applied Physics Vol.9 No.3
We report here the dielectric relaxation spectroscopy and electro-optical properties of a ferroelectric liquid crystal (FLC) CB470 (R) and isomeric mixtures containing CB470 (R) and its optical isomer CB480 (S) in two different concentrations. We have studied with two isomeric mixtures: mixing CB470 (R) and CB480 (S) in the ratio 95:5 (w/w) and 90:10 (w/w). With increase of percentage of CB480 (S) in the mixture the spontaneous polarization (PS) value has been decreased due to cancellation of a part of the dipolar contribution, since the direction of PS of the two isomers are in opposite direction. The tilt angles of the pure FLC materials and the isomeric mixtures remain almost unchanged. The dielectric strength of Goldstone mode is almost proportional to the spontaneous polarization (PS). An additional collective mode has been observed in the SmC* phase due to the formation of domain with large periodicity in pure FLC material and in one of the isomeric mixtures by unwinding the helical structures, which is known as domain mode. The existence of domain mode has been studied extensively with the variation of PS in the isomeric mixtures. The result has been discussed. We report here the dielectric relaxation spectroscopy and electro-optical properties of a ferroelectric liquid crystal (FLC) CB470 (R) and isomeric mixtures containing CB470 (R) and its optical isomer CB480 (S) in two different concentrations. We have studied with two isomeric mixtures: mixing CB470 (R) and CB480 (S) in the ratio 95:5 (w/w) and 90:10 (w/w). With increase of percentage of CB480 (S) in the mixture the spontaneous polarization (PS) value has been decreased due to cancellation of a part of the dipolar contribution, since the direction of PS of the two isomers are in opposite direction. The tilt angles of the pure FLC materials and the isomeric mixtures remain almost unchanged. The dielectric strength of Goldstone mode is almost proportional to the spontaneous polarization (PS). An additional collective mode has been observed in the SmC* phase due to the formation of domain with large periodicity in pure FLC material and in one of the isomeric mixtures by unwinding the helical structures, which is known as domain mode. The existence of domain mode has been studied extensively with the variation of PS in the isomeric mixtures. The result has been discussed.